Minimization of ring erosion during plasma processes

ABSTRACT

Methods are disclosed for etching a substrate. The method includes preferentially coating cover ring relative other chamber components in the processing chamber, while under vacuum, and while a substrate is not present in the processing chamber. The substrate is subsequently etched the processing chamber. After etching, the interior of the processing chamber is cleaned after the substrate has been removed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No.62/277,299, filed Jan. 11, 2016, of which is incorporated by referencein its entirety.

BACKGROUND OF THE DISCLOSURE

Field

The embodiments disclosed herein generally relate to controlling erosionof plasma processing chamber components and etching uniformity of asubstrate during plasma processing.

Description of the Background Art

Various semiconductor fabrication processes, such as plasma-assistedetching, physical vapor deposition, and chemical vapor deposition, amongothers, are often performed in plasma processing chambers in which asemiconductor work piece, such as a substrate, engages with a cover ringduring processing. For example in a plasma processing chamber configuredfor etching a semiconductor substrate, the substrate is mounted on asubstrate support pedestal within the processing chamber. The substratesupport pedestal includes a metal electrode to which an RF bias may beapplied. A plasma is formed from a mixture of process gases provided tothe processing chamber. The pressure within the processing chamber ismaintained by a pump which also removes by-products from the chamber. Apower supply is coupled to the electrode inside the substrate supportpedestal so as to produce on the electrode a negative bias voltagerelative to the plasma. The bias voltage attracts the charged ions fromthe plasma to bombard the substrate so as to etch the substrate duringprocessing. Because the electrode is negatively biased, the substratesupport pedestal is often called the cathode.

The substrate is positioned inward of the cover ring while supported onthe pedestal. Ions from the plasma gas formed in the chamber are biasedby the cathode to target the substrate. During etching, the ions fromthe plasma tend to impact the substrate disposed on the substratesupport at an angle normal to the plasma sheath. Over time, processequipment such as the cover ring, tend to erode from the ionbombardment. The erosion of the chamber components introducecontaminants into the chamber environment that substrate defects andshortens the mean time between maintenance as the chamber componentsmust be serviced or replaced. Additionally, the erosion of chambercomponents may cause the plasma sheath to bend in a manner such that thetrajectory of the plasma ions is no longer normal to the substrate. Forexample, erosion of the cover ring may cause plasma ions to angle towardthe side or underside of the substrate, thus contributing to poorprocessing results, particularly near the edge of the substrateproximate the cover ring.

Therefore there is a need for an improved method for plasma processingof substrates in etch chambers.

SUMMARY

In a first embodiment, a method is disclosed for etching a substrate.The method begins by coating an interior of a processing chamber withoutthe substrate present, the processing chamber having sidewalls, asubstrate support, and a cover ring. The cover ring is preferentiallycoated relative to the sidewalls and substrate support. The method alsoincludes etching a substrate disposed on the substrate support of theprocessing chamber after the interior of the processing chamber has beencoated. The method additionally includes cleaning the interior of theprocessing chamber while the substrate is no longer present and whilethe processing chamber remains under vacuum.

In a second embodiment, a method is disclosed for etching a substrate.The method begins by coating an interior of a processing chamber, nothaving a substrate therein, with a SiCl₄ coating. The processing chamberhas sidewalls, a substrate support, and a cover ring. The cover ring ispreferentially coated with the SiCl₄ relative to the sidewalls andsubstrate support. The method also includes etching a first substratedisposed on the substrate support of the processing chamber after theinterior of the processing chamber has been coated. The method alsoincludes removing the coating from the interior of the processingchamber while the first substrate is no longer present in the processingchamber. The method also includes repeating coating the interior of theprocessing chamber with a an interior of a processing chamber, nothaving a substrate therein, with a SiCl₄ coating after the SiCl₄ coatingpresent while etching the first substrate has been removed. The methodalso includes etching a second substrate disposed on the substratesupport of the processing chamber after the interior of the processingchamber has been coated.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of theembodiments herein are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

FIG. 1 depicts a plasma processing chamber having a substrate supportdisposed therein.

FIG. 2 depicts an enlarged portion of the processing chamber shown inFIG. 1 having a protective coating.

FIG. 3 is a flow diagram of a method for etching a substrate.

To facilitate understanding of the embodiments, identical referencenumerals have been used, where possible, to designate identical elementsthat are common to the figures. It is contemplated that elements andfeatures of one embodiment may be beneficially incorporated in otherembodiments without further recitation.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

Embodiments of the invention provide a method for etching a substrate.During the method for etching, a chamber coating is preferentiallyapplied to a cover ring disposed on a substrate support. Thepreferential application of the coating to the cover ring relative otherchamber components extends the life of the cover ring. The coatingdisposed on the cover ring also promotes process uniformity bymaintaining the horizontal consistency of the plasma sheath forconsistent process results. Additionally, preferentially coating of thecover ring mitigates both chamber contamination as well as mean timesbetween preventative maintenance.

FIG. 1 illustrates an exemplary processing chamber 100 suitable foretching a substrate therein. The exemplary processing chamber 100 issuitable for removing one or more film layers from the substrate 108. Itis contemplated that other process chambers, including those from othermanufactures, may be adapted to practice embodiments of the invention.

The processing chamber 100 includes a chamber body 105 having a chambervolume 101 defined therein. The chamber body 105 has sidewalls 112 and abottom 118, which are coupled to ground 126. The sidewalls 112 have acoating (discussed below in FIG. 2) utilized to protect the sidewalls112 and extend the time between maintenance cycles of the processingchamber 100. The dimensions of the chamber body 105 and relatedcomponents of the processing chamber 100 are not limited and generallyare proportionally larger than the size of the substrate 108 to beprocessed therein. Examples of substrate sizes include 200 mm diameter,250 mm diameter, 300 mm diameter and 450 mm diameter, among others.

The chamber body 105 supports a chamber lid assembly 110 to enclose thechamber volume 101. The chamber body 105 may be fabricated from aluminumor other suitable materials. A substrate access port 113 is formedthrough the sidewall 112 of the chamber body 105, facilitating thetransfer of the substrate 108 into and out of the processing chamber100. The access port 113 may be coupled to a transfer chamber and/orother chambers of a substrate processing system (not shown).

A pumping port 145 is formed through the sidewall 112 or bottom 118 ofthe chamber body 105. A pumping device (not shown) is coupled throughthe pumping port 145 to the chamber volume 101 to evacuate and controlthe pressure therein. The pumping device may include one or more pumpsand throttle valves. In one embodiment, the pumping device enables avacuum pressure between 10 and 30 mT to be maintained within the chambervolume 101.

A gas panel 160 is coupled by a gas line 167 to the chamber body 105 tosupply process gases into the chamber volume 101. The gas panel 160 mayinclude one or more process gas or cleaning gas sources 161, 162, 163,164 which may include inert gases, non-reactive gases, and reactivegases, if desired. Examples of process gases that may be provided by thegas panel 160 include, but are not limited to, silicon (Si), sulfur (S),fluorine (F₂), carbon (C), hydrogen (H), bromine (Br), hydrogen (H₂),argon (Ar), chlorine (Cl₂), nitrogen (N₂), oxygen (O₂), combinationsthereof or other suitable gases. The gas panel 160 may provide theprocess gases for etching, deposition or cleaning. For example, the gaspanel 160 may provide cleaning gases such as fluorine (Fl₂) for cleaningthe chamber volume 101 and process gases such as sulfur hexafluoride(SF₆) for etching.

Valves 166 control the flow of the process and cleaning gases from thesources 161, 162, 163, 164 from the gas panel 160. Operation of thevalves 166 are managed by a controller 165. The flow of the gasessupplied to the chamber body 105 from the gas panel 160 may includecombinations of the gases. For instance, the process gases SiCl₄ and O₂may be supplied into the processing volume to form a protective layer onchamber components inside the processing chamber 100.

The lid assembly 110 may include a nozzle 114. The nozzle 114 has one ormore ports for introducing the process and cleaning gases from the gaspanel 160 into the chamber volume 101. After the process gases areintroduced into the processing chamber 100, the gases are energized toform plasma. An antenna 148, such as one or more inductor coils, may beprovided adjacent to the processing chamber 100. An antenna power supply142 may power the antenna 148 through a match circuit 141 to inductivelycouple energy, such as RF energy, to the process gas to maintain aplasma formed from the process gas in the chamber volume 101 of theprocessing chamber 100.

A substrate support 132 is disposed in the chamber volume 101 on asubstrate support pedestal 135 to support the substrate 108 duringprocessing. The substrate support pedestal 135 may have a cathode liner136 to protect the sidewalls of the substrate support pedestal 135 fromthe plasma gases and to extend the time between maintenance of theprocessing chamber 100.

A cooling base (not shown) may be provided to assist in controlling thetemperature of the substrate 108. To mitigate process drift and time,the temperature of the substrate 108 may be maintained substantiallyconstant by the cooling base throughout the time the substrate 108 is inthe etch chamber. In one embodiment, the temperature of the substrate108 is maintained throughout subsequent etch processes at about 90degrees Celsius.

The substrate support 132 may have a dielectric body 122. A chuckingelectrode 121 for holding the substrate 108 during processing may beembedded in the dielectric body 122. The chucking electrode 121 useselectro-static attraction to hold the substrate 108 to the substratesupport pedestal 135. The chucking electrode 121 is powered by an RFpower supply 125 integrated with a match circuit 124. The RF powersupply 125 may provide a RF chucking voltage of about 200 volts to about2000 volts to the chucking electrode 121.

The substrate support 132 may also include cathode electrodes 151, 153deposed within the dielectric body 122. The cathode electrodes 151, 153are coupled to a power source 150 and provide a bias which attractsplasma ions, formed by the process gases in the chamber volume 101, tothe substrate support 132 and substrate 108 positioned thereon. Thepower source 150 may cycle on and off, or pulse, during processing ofthe substrate 108. The power source 150 may independently operate thecathode electrodes 151, 153. In one embodiment, the power source 150provides the cathode electrodes 151, 153 with between about 200 Watts toabout 1000 Watts of RF power for processing the substrate 108.

The substrate support 132 may include heaters 172, 174 disposed thereinand connected to a power source 176, for heating the substrate. Thesubstrate support 132 is configured to perform in the temperature rangerequired by the thermal budget of the device being fabricated on thesubstrate 108. For example, the substrate support 132 may be configuredto maintain the substrate 108 at a temperature of about minus about 25degrees Celsius to about 500 degrees Celsius for certain embodiments.

A cover ring 130 is disposed on the substrate support 132, along theperiphery of the substrate support pedestal 135. The cover ring 130 isconfigured to promote etching uniformity at the edge of the substrate108, while shielding the top surface of the substrate support pedestal135 from the plasma environment inside the processing chamber 100. Liftpins (not shown) are selectively moved through the substrate supportpedestal 135 to lift the substrate 108 above the substrate supportpedestal 135 to facilitate access to the substrate 108 by a transferrobot (not shown) or other suitable transfer mechanism.

The chamber components exposed to the chamber volume 101 may have acoating thereon to protect the chamber components from erosion. Thecoating prevents the degradation of the chamber components which in turnaffect processes conducted in the chamber volume 101. The coatingmitigates erosion of the chamber components such as the sidewall 112 andthe cover ring 130. Thus, the coating helps mitigate the introduction ofcontaminants into the chamber volume 101 and extends the meantimebetween preventative maintenance.

FIG. 2 depicts an enlarged portion of the processing chamber 100 in FIG.1 illustrating a portion of the substrate support pedestal 135 and aportion of the sidewall 112. The cover ring 130 disposed on thesubstrate support pedestal 135 may have one or more parts. In oneembodiment, the cover ring 130 is a single ring. In another embodiment,the cover ring 130 has an inner ring 232 that abuts an outer ring 234.The inner ring 232 may be formed from a material such as a carbide orsilicon (e.g., SiC), quartz, SiO_(x), or other suitable material. In oneembodiment, the inner ring is formed from SiC. The outer ring 234 maysimilarly be formed from quartz or other suitable material. The innerring 232 is disposed inside the outer ring 234, distally from thesidewall 112, and configured to closely circumscribe the substrate 118during processing. As the plasma is centrally located above thesubstrate 118 during processing, the inner ring 232 is more exposed tothe charged ions in the plasma attracted to the substrate 108 undergoingprocessing then other chamber components including the outer ring 234.

A sheath 260 is formed at the edge of the plasma by positively chargedions 262. The sheath 260 is substantially conformal to the topology ofthe negatively charged surface, e.g., the substrate support pedestal 135and/or substrate 108. Wear in the surface of the cover ring 130 and inparticular the inner ring 232 may create irregularities or bend thesheath 260. Generally, the charged ions 262 of the plasma move in adirection normal to the sheath 260. Thus, it is advantageous to maintainthe sheath 260 perpendicular to some surfaces undergoing processing,such as the top surface of a substrate 108 undergoing etch processing toform deep vias.

A protective coating 242 is provided on the inner ring 232 to mitigateerosion or the inner ring 232 from the plasma ions. The protectivecoating 242 substantially prevents erosion of the inner ring 232 at theedge of the substrate 108. Thus, the protective coating 242 mitigatesbending of the sheath 260 at the outer edge of the substrate 108 andsubstantially prevents non-uniformity and defects in the substrate 108along the outer edge of the substrate 108 near the inner ring 232.

Other chamber components also have a protective coating 244, 206. Theprotective coating 206 disposed on the sidewall 112 and the protectivecoating 244 disposed on the substrate support pedestal 135 are formed atthe same time as the protective coating 242 is formed on the inner ring232. The coatings 242, 244, 206 may be formed from SiO_(x), a carboncontaining material, such as with CH₄ or a fluorocarbon gas, such asC₄F₆ or C₄F₈, or other suitable material. The coatings 242, 244, 206 maybe formed while the processing chamber 100 is under vacuum before thesubstrate 108 enters the processing chamber 100 for etching. Thecoatings 242, 244, 206 may be removed while the processing chamber 100is under vacuum when cleaning the chamber 100. The processing chamber100 may be performed after etching a predefined number of substrates,for example one or more, and occurs after the substrate 108 has beenremoved from the processing chamber 100. This process of forming andremoving the coatings 242, 244, 206 is discussed in further detail belowin reference to FIG. 3.

Continuing with the discussion of FIG. 2, the protective coating 242 onthe inner ring 232 is exposed to more charged ions 262 and thus theprotective coating 242 is attacked more aggressively than the othercoatings 244, 206 on the other chamber components, including the outerring 234. The coating 242 is formed in-situ along with and at the sametime as the other coatings 244, 206. However, the coating 242 ispreferentially formed of a higher quality and/or thickness relative tothe coatings 244, 206.

For the Si based coatings, the cathode electrode 153 may independentlybias the inner ring 232 relative to the center regions of the substratesupport 132. For example, the substrate support 132 and the outer ring234 may not be biased or have a significantly lower bias than thatapplied to the inner ring 232. The cathode electrode 153 may create ionenergy at the inner ring of about 40 eV to about 100 eV whereas the ionenergy at the other chamber components such as that at the outer ring234 and the substrate support 132 may be about 15 eV or less. Thus, thecharged ions of the plasma may be preferentially attracted to the innerring 232 by the cathode electrode 153 to form the coating 242.

For the carbon based coatings, higher temperatures promote denser films.The density of the carbon based coatings is similar to the density ofthe SiO_(x) coatings. Increased bias power does not preferentiallyincrease the quality and/or thickness of carbon based coatings formed onthe inner ring 232. Therefore, increasing the temperature of the coverring 130 increases the quality of the carbon based coatings formed onthe inner ring 232 for the carbon based coatings. For example, the powersource may supply between about 300 Watts and about 1500 Watts to theheater 174 to increase the temperature of the inner ring 232 to achievea denser film relative to the carbon based coatings formed on otherchamber components.

The result of the preferential formation of the coating 242 is thatcoating 242 has a thickness 240 which is greater than a thickness 250 ofthe coating 206 formed on the sidewall 112. The coating 242 is also of ahigher density then the other coatings 244, 206. The coating 242 may beabout 10 to about 30 times denser than the other coatings 244, 206formed on the other chamber components. The higher quality of thecoating 242 may offer about 10 times to 100 times more etch resistantthan the other chamber coatings 244, 206.

During processing, the coating 242 may be more aggressively attacked bythe charged ions 262 biased to the substrate 108 relative to the coating244, 206 present on other chamber components. However, due to the higherquality of the coating 242, the coating 242 is better able to withstandthe impact from the charged ions 262 relative to the coatings 244, 206protecting the other chamber components from erosion by the plasma ions.Advantageously, the coating 242 promotes process uniformity bymaintaining the horizontal consistency of the sheath 260 for consistentprocess results of the substrates 108. Additionally, the coatings 242,244, 206 improve the mean-time between maintenance by significantlyreducing erosion of chamber components from the etchants.

FIG. 3 depicts a flow diagram of a method 300 for etching a substrate.The method 300 begins at block 310 by coating an interior of aprocessing chamber while the processing chamber is maintained undervacuum. There is no substrate present in the processing chamber whilethe processing chamber is being coated. The processing chamber hassidewalls, a substrate support, and a cover ring. The cover ring ispreferentially coated relative to the sidewalls and substrate support.

In one example, the cover ring is preferentially coated relative to thesidewalls and substrate support by biasing the cover ring with a cathodeelectrode. In another example, the cover ring is preferentially coatedrelative to the sidewalls and substrate support by biasing the coverring with a cathode electrode with more bias power relative to a biaspower applied to a center region of the substrate support. In thismanner, a ring coating is formed which is thicker and denser than achamber coating formed on other chamber components in the interior of aprocessing chamber. The etchants come into contact and attack thechamber components. The coating is formed on the cover ring to athickness selected to prevent the cover ring from being attacked duringsubsequent etching of the substrate. Biasing the ring coating produces ahigher quality coating as well. The ring coating may also be about 10 toabout 30 times denser than the coating on other chamber components.Thus, the ring coating may be about 10 times to 100 times more etchresistant than coating disposed on other chamber components.

In one example, O₂ and SiCl₄ process gasses may be provided to form aSiO_(x) coating within the processing chamber. A ratio of the O₂ toSiCl₄ process gasses is maintained below 1. In another example, a carbonbased process gas may be supplied to form a carbon based coating withinthe processing chamber. A power source provides greater than 1000 W formaintaining the plasma in the processing chamber. The power supply maygenerate up to about 15 eV ion energy.

In some examples, the cover ring has an inner ring and an outer ring. Acathode electrode is disposed along a periphery of the substrate supportto provide increased ion energy at the inner ring relative to regions ofthe substrate support disposed inward of the inner ring. The cathodeelectrode substantially overlaps vertically with the inner ring andcreates ion energy at the inner ring of about 40 eV to about 100 eV. Thecoating on the inner ring may also be thicker than the coating on theouter ring or the substrate support.

In some embodiments, a dummy wafer may be disposed on the substratesupport to prevent the formation of the coating on the region of thesubstrate support disposed below the substrate during processing. Thedummy wafer may be used in those embodiments wherein the substratesupport has only a single cathode electrode disposed in body of thesubstrate support and configured to attract ions to a substrate duringprocessing. The dummy wafer may protect the central area of thesubstrate support from being coated. The dummy may also be used inembodiments having the cathode electrode disposed along a periphery ofthe substrate support. In this manner the central area of the substratesupport is protected from being coated.

Preferentially coating the cover ring may alternately or additionallyinclude heating the inner ring of the cover ring to a temperaturegreater than either an outer ring of the cover ring or the other chambercomponent. The coating preferentially forms on the higher temperature ofthe inner ring.

In another example wherein carbon based coatings are formed, the coverring may be preferentially heated relative to other chamber component toproduce a higher quality and/or thickness coating on the cover ringrelative to other chamber components. In one example, the inner ring ofthe cover ring may be heated to a temperature greater than at least oneor more of the outer ring, the center region of the substrate supportthat is disposed inward of the cover ring or the other chambercomponent.

In a second block 320 of the method 300, a substrate disposed on thesubstrate support of the processing chamber is etched in the presence ofthe coated cover ring. The substrate is moved into the processingchamber and placed on the substrate support by a robot or throughanother manner. Etchants may be introduced into the chamber forselectively removing material from the substrate. In one embodiment, HBrand O₂ processes gases are introduced into the interior volume of thechamber to form reactive species (etchants) for etching a feature, suchas a trench or via, into the substrate. Process parameters dictate theformation of the features in the substrate. The coating protecting thechamber components must be able to withstand the etchants until thecompletion of the features formed during the process cycle. The etchantscome into contact and attack chamber components. However, the etchantsare biased toward the substrate and attack those chamber componentsclosest to the substrate, such as the inner ring, more aggressively.Thus, the higher quality and thickness of the coating on the inner ringis selected to protect the inner ring from damage while the substrate isetched. In some embodiments, the coating formed at block 310 is SiC whena dielectric material is etched at block 320. In some embodiments, thecoating formed at block 310 is a carbon based coating when a conductivematerial or silicon is etched at block 320.

In a third block 330 of the method 300, the interior of the processingchamber is cleaned while the processing chamber remains under vacuum.Cleaning may be performed between etching of each substrate or afteretching a number of substrates. The substrate is not present in theinterior of the processing chamber while the processing chamber iscleaned. The substrate is removed from the processing chamber by a robotor other manner. A cleaning gas, such as fluorine (Fl), chlorine (Cl) ora derivative thereof, may be introduced into the processing chamber forremoving contaminants as well as the coating from the chamber componentssuch as the walls and the cover ring. The material and byproductsremoved from the chamber components by the cleaning gas may be pumpedout of the chamber by the vacuum.

After cleaning the chamber, the method 300 may repeat the processesdescribed at block 310, block 320 and block 330. In some embodiments,the processes described at block 310 are performed prior to etching asubsequent substrate. In this manner, the chamber may be cleaned ofpotential contaminants prior to the processing for each substrate.Additionally, the chamber components can be re-coated to prevent wearand erosion. Thus, extending the mean time between preventativemaintenance and the bringing the processing equipment offline. Thebenefit achieved by both these advantages translates to overall higherquality and throughput while generating overall cost savings infabrication.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow:

What is claimed is:
 1. A method for etching a substrate comprising:coating an interior of a processing chamber without a substrate presentand while the processing chamber remains under vacuum, the processingchamber having sidewalls, a substrate support, and a cover ring, whereinthe cover ring is preferentially coated relative to at least thesubstrate support and a top surface of the substrate support is exposedduring the coating of the interior of the processing chamber; etching asubstrate disposed on the substrate support of the processing chamber inthe presence of the coated cover ring; and cleaning the interior of theprocessing chamber while the processing chamber remains under vacuum andwhile the substrate is no longer present in the interior of theprocessing chamber.
 2. The method of claim 1, wherein preferentiallycoating the cover ring comprises: biasing the cover ring.
 3. The methodof claim 1, wherein preferentially coating the cover ring relative to atleast the substrate support further comprises: forming a coating on thecover ring that is about 10 times to about 30 times denser than acoating formed on the sidewalls.
 4. The method of claim 1, whereinpreferentially coating the cover ring relative to at least the substratesupport further comprises: forming a coating that is about 10 times toabout 100 times more etch resistant than a coating formed on thesidewalls.
 5. The method of claim 1, wherein coating the interior of theprocessing chamber further comprises: coating an inner ring and an outerring of the cover ring.
 6. The method of claim 5, wherein coating theinner ring and the outer ring further comprises: coating the inner ringwith a coating that is thicker than a coating formed on the outer ring.7. The method of claim 1, wherein preferentially coating the cover ringrelative to at least the substrate support further comprises: biasingthe cover ring with a cathode electrode that is disposed along aperiphery of the substrate support, the cathode electrode substantiallyoverlapping vertically with the inner ring.
 8. The method of claim 1,wherein preferentially coating the cover ring comprises: heating aninner ring of the cover ring to a temperature greater than either atemperature an outer ring of the cover ring or a temperature of thesidewalls.
 9. The method of claim 1, wherein preferentially coating thecover ring comprises: providing greater than about 1000 W of power tomaintain a plasma in the processing chamber.
 10. The method of claim 1,wherein preferentially coating the cover ring comprises: forming aSiO_(x) coating from process gasses comprising O₂ and SiCl₄.
 11. Themethod of claim 10, wherein a ratio of O₂ to SiCl₄ process gasses ismaintained below
 1. 12. The method of claim 1, wherein preferentiallycoating the cover ring comprises: forming a carbon based coating.
 13. Amethod for etching a substrate comprising: A) coating an interior of aprocessing chamber while under vacuum with a SiCl₄ coating without asubstrate being present in the processing chamber, the processingchamber having sidewalls, a substrate support, and a cover ring, whereinthe cover ring is preferentially coated with the SiO_(x) relative to thesidewalls; B) etching a substrate disposed on the substrate support ofthe processing chamber; C) removing the coating from the interior of theprocessing chamber while under vacuum and while the substrate is nolonger present in the interior of the processing chamber; andsequentially repeating A), B) and C).
 14. The method of claim 13,wherein preferentially coating the inner cover ring comprises: forming aplasma from O₂ and SiCl₄ process gasses; biasing the cover ring with acathode electrode; and coating the cover ring with a thicker and densercoating of SiO_(x) than the SiO_(x) coating formed on other chambercomponents in the interior of a processing chamber.
 15. The method ofclaim 14, wherein the SiO_(x) coating the cover ring is about 10 toabout 30 times more dense than the SiO_(x) coating the sidewalls. 16.The method of claim 15, wherein the SiO_(x) coating disposed on thecover ring is about 10 times to 100 time more etch resistant than theSiO_(x) coating on the sidewalls.
 17. The method of claim 14, whereinbiasing further comprises: biasing a cathode electrode is disposedvertically below the cover ring.
 18. The method of claim 14, wherein aratio of O₂ to SiCl₄ process gasses is maintained below
 1. 19. Themethod of claim 13, wherein preferentially coating the inner cover ringcomprises: maintaining a plasma in the processing chamber using greaterthan about 1000 W of power.